This invention relates to canning of electric motors for use in submerged operation.
Conventional motor rotors and stators are canned using non-magnetic metallic material. Often sheet metal having a thickness of 0.025 inch or more is used on the periphery of the motor rotor and on the interior surface of the motor stator. Magnetic flux passing between the rotor and the stator introduces eddy currents in conductive material such as metallic canning material that reduce the motor efficiency and, in some cases, require an increase in the size of the motor. Heretofore, such eddy current losses have been overcome by encapsulating the rotor and stator in a single layer of composite material but this has been found inadequate to provide sufficient resistance to leakage while also providing the necessary strength to resist damage.
The Blakeley et al. U.S. Pat. No. 5,122,704 discloses a composite rotor sleeve arranged to preclude flow of liquid between a liquid-cooled rotor and the air gap between the rotor and the stator in an electric motor while preventing relative movement between the sleeve and the rotor as a result of thermal cycling. For this purpose the sleeve, which is preferably pre-fabricated and applied with an interference fit onto the rotor, is made up of a radially inner component which is continuous film of polyimide material and may be a helically wound ribbon sealed with a polyimide adhesive and a cylindrical element formed of a plurality of plies of wound fibrous material such as carbon fiber with each ply being impregnated in a resin matrix. Preferably, the resin is a polyimide resin to provide high temperature resistance. In a preferred embodiment, the cylindrical element has twelve plies, eight being wound generally circumferentially to provide a high measure of hoop strength and the remaining four being wound at a pre-determined angle to prevent generation of thermally induced stresses or relative movement between the sleeve and the rotor. The combined fibrous layers provide the strength to hold the rotor components in position while the continuous film layer precludes flow of liquid between the rotor component and the space between the rotor and stator.
The Smith U.S. Pat. No. 6,069,421 discloses an electric motor having a composite encapsulated stator and a composite encapsulated rotor, each of which is enclosed in a canning layer of high strength resin containing high modulus fibers, such as fiberglass, graphite, carbon, boron, quartz or aramid fiber material, combined with a metallic backing ring on the side away from the magnetic flux field extending between the rotor and the stator.
The Dohogne U.S. Pat. No. 4,973,872 discloses a rotor assembly having a plurality of magnets encapsulated by an outer molded plastic cylindrical sleeve having runners which extend into channels in the rotor core. The plastic sleeve may be a fiberglass-filled plastic material.
According to the Brown U.S. Pat. No. 4,930,201, a permanent magnet rotor is surrounded by a sleeve made of composite material which includes high strength, high modulus fibers such as fiberglass, graphite, boron and kevlar embedded in an epoxy or other plastic matrix which may be made by wet winding of high strength filaments onto the rotor assembly followed by curing or by forming the composite sleeve on a mandrel and subsequently shrinking it onto the rotor.
The Patel U.S. Pat. Nos. 4,633,113 and 4,674,178 disclose permanent magnet rotors surrounded by a body of cured fibrous material formed by winding a fiber such as carbon fiber in a curable resin such as epoxy resin circumferentially about the rotor structure and curing the epoxy material, which may be followed by application of a layer of epoxy resin to the outer surface which is then cured.
In the Nashiki et al. U.S. Pat. No. 4,433,261 a permanent magnet rotor is bound with non-magnetic fibers such as glass fiber or carbon fiber and then secured with resin to prevent peeling off of the magnets.